Synthetic strap

ABSTRACT

Synthetic strapping made up of two layers of synthetic filament yarns with a bonding band formed of compatible synthetic material located between these layers and fusion bonded to the surfaces of the yarns with which the band is in contact, some of the band material extending into spaces between the yarns and into spaces between the filaments of the individual yarn.

United States Patent [72] lnventor James A. Kippan 3,028,281 4/1962 Karass 161/143 440 Brooksbank Ave., North Vancouver, 3,095,338 6/ 1963 Romanin 161/142 British Columbia, Canada 3,248,274 4/1966 Karass.... 161/143 X [21] Appl. No. 778,483 3,276,944 10/1966 Levy 161/402 X [22] Filed Nov. 25, 1968 3,391,050 7/1968 Nebesar 161/60 X [45] Patented Nov. 23, 1971 3,459,615 8/1969 Eilerman 156/181 3,475,264 10/1969 Donaldson 161/60X 3,314,841 4/1967 Romanin.... 161/143 X 1 SYNTFETIC STRAP 3,526,565 9/1970 Walter 161/86 X 14 Claims 7 Drawing Primary Examiner- Robert F. Burnett [52] US. Cl 1 61/60, Ass/slam E mminer inda C Koeckert 57/144, 61/143, l61/146 Attorney-Fetherstonhaugh & Co. [51] int. Cl B32b 5/12 [50] Field of Search 156/167,

176, 178, 181, 297; 161/55, 57, 60, 46, 47, 140, ABSTRACT: Synthetic strapping made up of two layers of 142, 143, 144, 146, 148, 159; 57/140, 144 synthetic filament yarns with a bonding band formed of compatible synthetic material located between these layers and ful References Clted sion bonded to the surfaces of the yarns with which the band is UNITED STATES PATENTS in contact, some of the band material extending into spaces 2,098,909 11/1937 Angier l61/14OX between the yarns and into spaces between the filaments of 2,636,835 4/1953 Boulware et a1. 161/140 mdwldua' yam 2,974,559 3/1961 Coggi l61/176X 3,":- r- 1 ll -29 J l I 1 is 3 U j 27 '5 I l 25 SYNTHETIC STRAP BACKGROUND OF THE INVENTION This invention relates to synthetic strapping and to methods of producing this strapping. The term strapping as used herein and in the accompanying claims includes straps such as commonly used for the purpose of binding together, holding in place, lifting and general handling of packages, pallets, lumber, pipe, general cargo and the like.

Metal strapping has generally been used for binding large packages, boxes and the like, but this strapping is relatively expensive, difficult to handle, subject to corrosion, and subject to breakage if unduly flexed. Some effort has been made to produce synthetic strapping for these purposes, but these have not been overly successful for financial or other reasons.

Heretofore, polyolefin straps, and particularly polypropylene straps, have been produced mainly by a process of extruding a band of polyolefin, quenching, heating and stretching under controlled heat to orient the molecular structure and thus impart greatly improved tensile strength. Straps so produced are solid or of one piece and are generally rectangular in cross section. A disadvantage of such solid straps is the practical limit to size or cross-sectional area that can economically be produced. The limiting factor is the degree of molecular orientation and resultant unit tensile strength obtainable in a polyolefin rectangular section of the required thickness. The amount of molecular orientation obtainable is inversely proportional to the thickness of the cross section. A second disadvantage of solid polypropylene strapping is the difficult joining together of strap ends and most particularly in large size strapping. Because of the unidirectional molecular orientation of the strap, it possesses low shear strength in the longitudinal direction of the strap. When a standard compression seal, as common to steel and nylon strapping, is used for joining, the seal exerts maximum compression forces at the edges of the strap and minimum compression forces in the center portion of the strap. Such uneven forces cause uneven tensile stresses in the strap when loaded with resultant shear failure or fibrillation in the center section of the strap.

To minimize shear or fibrillation failure, types of seals have been developed which completely surround the overlapped strap ends and are applied with a crimpling action that tends to exert as much pressure as possible on the center section of the strap. While the efficiency of such seals is adequate for straps of under 1% inch in width the efficiency becomes less in wider straps unless the weight and size of the seal is increased above economic efliciency. As the seal size and weight increases, there results equivalent inefficiency and difficulty of seal application. Because of these difficulties in mechanically LII sealing polyolefin strap ends, there have been developed alter native welding techniques that essentially cause fusion bonding of the overlapping strap surfaces. The fusion bonding or welding techniques so employed must be such as to cause sufficient heat generation to fuse opposing strap surfaces without the heat penetrating sufficiently to disturb the oriented molecular structure of the strap and thus reduce its tenacity. Present fusion bonding or welding techniques are limited to strap widths not exceeding 1% inches because of the extreme difficulty of consistently supplying suflicient heat over large strap areas to insure proper bonding without overheating. The inclusion of either moisture or foreign material between strap surfaces to be welded also greatly affects the efficiency of the welded joint. Several attempts have been made unsuccessfully to glue or solvent-weld polyolefin strap joints. At present there is no commercially available glue or solvent for this purpose.

In the past, flexible straps have been produced by the commonly known method of weaving together yarns or threads of both natural and synthetic fibers. The main disadvantage of such straps is their high cost which relates directly to the cost of the weaving process. A further disadvantage of woven straps is the stretch or elongation of such straps under load. In woven straps, the warp threads or yarns are required to assume almost the total applied load and in so doing, tend to form straight lines displacing the woof threads or yarns with resultant elongation and transverse contraction.

Flexible straps are also produced by the commonly known method of flat braiding natural or synthetic yarns. The main disadvantage is the relatively high cost thereof due to the slow speed of braiding production. A further marked disadvantage is the high stretch of such straps. Stretch is caused by the yarns attempting to form straight lines under load with resultant trap elongation and marked shrinkage in cross-sectional width.

Heretofore, straps have also been produced by a method of gluing or bonding a plurality of parallel threads or yarns of natural fibers, synthetic fibers, twisted paper and the like. Such straps are in general use in relatively small sizes. The main disadvantage of these straps is their relatively high cost. A further disadvantage of the glued or bonded straps is the stiflness of such straps, particularly in large sizes. Another disadvantage is that most glues crack when the strap is tightened around comers.

Attempts have been made to produce polyolefin straps of multi yam construction by extruding a hot sheath of polyolefin around a central core of polyolefin yarns laid parallel and side by side. The sheath of polyolefin of such compatibility as to fusion bond to the fiber yarns when applied at appropriate high temperature and pressure will form a permanent bond to the encased outer fibers of the yarns. The main disadvantage of such construction is the stiffness created when the sheath is bonded to the yarns. An additional disadvantage is that such straps have a marked tendency to crack in a longitudinal direction under load. Another disadvantage is the added weight of the continuous sheath required for the simple purpose of containing the yarns, and the resultant economic inefficiency of the product. The additional disadvantage is the joining of strap ends which exhibit similar characteristics to solid polyolefin straps as outlined above.

SUMMARY OF THE INVENTION A synthetic strap in accordance with the present invention comprises two layers of synthetic filament yarns extending longitudinally of the strap, and a bonding band formed of synthetic material compatible with the material of said yarns and located between the yarn layers and contacting all of the yarns thereof and fusion bonded to the portions of the surfaces of the yarns with which the band is in contact. With this ar rangement, some of the band material extends into spaces between the yarns and into spaces between the filaments of the individual yarns so that the band bonds the yarns of each layer together and the layers to each other without interfering with the natural flexibility of the yarn. As the material of the bonding band is compatible with that of the yarn filaments, the band flexes with the yarns without danger of cracking or separating therefrom. The bonding band is preferably in the form at least one relatively narrow, thin band extending generally longitudinally of the strap in a zigzag pattern. In the preferred synthetic strap there are a plurality of zigzag-bonding bands arranged to form diamond-shaped openings between the yarn layers. The yarns and the bonding band or bands are preferably formed of a polyolefin or copolymer thereof, usually polyethylene or polypropylene. The strap can be strengthened by including at least one thread extending generally longitudinally thereof in a zigzag pattern between and contacting the yarn. The thread is formed of a material that fuses at a temperature above the fusion temperature of the bonding band material and yet adheres to said band material. In other words, the bonding band material holds the thread in place, but the latter does not melt when it comes into contact with the hot band material during manufacture of the strap. For example, the thread can be made of nylon, fiberglass or any other suitable material that is practically nonextensible. The thread, preferably arranged in a zigzag pattern that does not coincide with the pattern of the bonding band, reinforces the strap in a transverse direction.

Synthetic strapping produced in accordance with this invention is more flexible, possesses a higher strength to weight ratio, and may be more economically produced in larger sizes than any synthetic strapping heretofore on the market. This strapping can be produced at a higher linear speed than any heretofore commercially obtainable. This strapping has hightensile capacity, high useful elongation and high-energy absorption. It is quite flexible, is resistant, to rot and corrosion, and is relatively nonabrasive to the corners of contained packages, such as lumber, boxes, general cargo and the like. In addition, the present strapping has superior joining characteristics.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a substantially diagrammatic perspective view of a synthetic strap in accordance with this invention,

FIG. 2 is a diagrammatic section taken on the line 2--2 of FIG. 1,

FIG. 3 is a diagrammatic perspective view of an alternative form of yarn that can be used in this strap,

FIG. 4 is a diagram illustrating the zigzag pattern of the bonding band in one embodiment of the invention,

FIG. 5 is a diagram illustrating the zigzag pattern of the bonding band in another embodiment of the invention,

FIG. 6 is a view similar to FIGS. 4 and 5 illustrating a zigzag pattern of still another embodiment of the invention, and

FIG. 7 is a diagrammatic side elevation of a strap bent to fit around a corner.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The drawings are of necessity diagrammatic since it is very difficult to illustrate small yarns made up of bundles of monofilament or filaments. Thus, the drawings can only roughly illustrate the invention, but they do help one to understand the construction of the various synthetic straps.

Referring to the drawings, 10 is a synthetic strap made in accordance with the present invention, and includes two layers 11 and 12 of yarns l3 placed side-by-side in each layer. Each yarn 13 can be any yarn made up of synthetic material. In strap 10, each yarn 13 is made up of a bundle of filaments 15 which extend generally longitudinally of the yarn and, in this example, the filaments have a slight spiral twist along the yams to keep them together.

A bonding band 18 is located between yarn layers 11 and 12 and is formed of a synthetic material compatible with the material of the yarns. The material of the bonding band and of the yarn must be compatible so that they both react the same way to heat. The tenn compatible is used to indicate material that will fuse with synthetic filaments, and that has similar physical and chemical characteristics, that is, as to flexibility and resistance to attack by acids, rotting and the like. This bonding band may be in the form of a thin layer positioned between the yarn layers and extending from side 20 to side 21 of the strap. However, it is preferable to make the bonding band in the form of at least one narrow and thin band which extends generally longitudinally of the strap in a zigzag pattern from side to side thereof, as clearly shown in FIG. I. In this Figure, bonding band 18 is formed of at least one narrow band 24 which extends angularly back and forth across the strap from side 20 to side 21 thereof. In this example, the bonding band is made up of at least two of the these bands, the second of which is designated by the numeral 25. As bonding bands 24 and 25 are arranged in zigzag patterns, they cross each other repeatedly throughout the length of the strap and form open-centered diamonds 27. Although the angular arrangement of the bands may be as desired, it has been found that very good results are attained if each diamond 27 is formed with its diagonal 29 extending longitudinally of the strap no longer than, and preferably shorter than, the length of diagonal 30 extending transversely of the strap.

The size and number of yarns used in the strap are dependent upon the width, thickness and strength of the strap required. It is preferable, but not mandatory, to use the same size and number of yarn 13 in both layers 11 and 12 of the strap. The band or bands of bonding band 18 are applied to the opposing faces of the two yarn layers. The filaments of the yarns are preferably made of polyolefin or a copolymer thereof, and of these polyethylene or polypropylene or the copolymers thereof are preferred. The synthetic material of band 18 must be compatible with that of the yarn filaments, and it is usually the same material as the yarn filaments. The band material is cast while molten and not subject to undue force after cooling and is, therefore, in a cast or nonoriented molecular state. The filaments of yarns 13 are preferably oriented when the yarn are being made.

Strap 10 can be made in any desired manner, and its production would not present any problem to one skilled in the art. The individual bonding bands 24 and 25 can be extruded on to the yarn layers by means of movable dies with appropriate number and size of apertures to produce the required number and size of bands. These bands, being in molten state during application, fuse one to the other at intersections 32. The molten material of the individual bonding bands extends into the spaces 35 between yarns l3 and into spaces 36 between the filaments 15 of the individual yarn so that the bands bond the yarns of each layer together and the layers to each other without interfering with the natural flexibility of the yarns.

The molten material for the bonding band or bands can be applied to the surfaces of the yarn layers hat are to be brought together by a movable die attached to a continuous source of molten material a movable such as a standard plastic extruder common to the industry. The two layers of yarns are brought together under modest pressure in any convenient way, such as by a pair of spring-loaded rollers. The contact of the two yarn layers with the molten band material thereon causes the required fusion bonding of the two yarn interfaces. To insure the predetermined depth of bonding and to avoid excess heat damage to the oriented structure of the yarn filaments, the strap is quenched, for example, in a water bath immediately following the transverse pressure application by the rollers of the like.

As stated above, the number and size of bonding bands applied is relative to the strap width and desired flexibility. For example, a strap constructed from two layers of polyolefin yams of, for example, zfi-ineh strap width and of yarns of, for example 5,000 to 10,000 denier per yarn, would ideally have two individual bonding bands of a thickness of, for example, about 0.002 to about 0.075 inch, and a width of about 0.010 inch to about 0.125 inch. As a further example, a strap constructed with two layers of polyolefin yarns of say 2-inch width and yarns of 20,000 denier per yarn would normally require about four individual bonding bands of a thickness from about 0.005 inch to about 0.100 inch, and a width of from about 0.020 inch to about 0.500 inch. Another example would be the use of eight bonding bands in a 6-inch wide strap consisting of two layers of yarn of, for example, 15,000 to 75,000 denier per yarn in which the band thickness would be from about 0.010 inch to about 0.200 inch, and the band width from about 0.050 inch to about 0.700 inch. in order to secure optimum transverse strength of the strap, it is desirable to limit the length of the longitudinal diagonal 29 of each diamond to about 2, inches or less.

The bonding bands of compatible material are applied to the opposing faces of the yarn layer at a temperature, for example, from about 450 F. to about 625 F and a pressure, for example, from about 250 to about 2,500 p.s.i. to cause the band material to fuse with the filaments of the yarn.

Bands 24 and 25 of strap 10 are firmly bonded to the opposing faces of the yarn layers only at their points of contact with the yarns and not throughout the total length or circumference of the yarn, thereby bonding the yarns to each other while allowing the strap maximum flexibility. The bonding bands are located midway between the outer faces of the strap at the central transverse axes thereof.

By referring to FIG. 2, it will be seen that the majority of the filaments 15 of yarns 13 are not in contact with the material of bonding band 18 so that said filaments are free to move relative to each other. Thus, when the strap is flexed or bent, this relative movement of the yarn filaments keeps the resistance to the bending action to a minimum. There can also be some relative movement between portions of all of the yarns. FIG. 7 shows strap 10 bent as it would be around a right angle comer. The filaments of the yarns of outer layer 11 move inwardly radially around the bend 40 while the filaments of the yarns of inner layer 12 are free to flex inwardly radially as indicated at 41. In other words, the inner filaments can be displaced relative to the inner surface of the strap, which would not be the case if the yarns used were solid or if the filaments of the yarns were stuck to each other.

By referring to FIG. 1, it will be seen that part of the longitudinally extending yarns are completely free from any restraint relative to each other and to the bonding band within diamonds 27, as indicated at 43. This helps in providing maximum flexibility for the strap, and yet the yarns are securely held together, as are the two layers of the strap. As stated above, a single bonding layer 18 extending the full width of the strap may be used, but this is not nearly as good as the zigzaging bonding band or bands illustrated, since the resulting strap would have considerably less flexibility. If a single, full-width bonding band were used, the cross section of the strap would be substantially the same as shown in FIG. 2, and the material of this band would be fused to the yarn filaments with which it is in contact.

Any force trying to pull the yarns of the strap away from each other in a lateral direction is resisted by the portions of the bonding bands which extend diagonally across the strap from side to side thereof. The lateral force would be pulling substantially longitudinally of the diagonal bands.

FIG. 3 diagrammatically illustrates an alternative yarn 45 which may be used in place of yarns 13 of strap 10. Yarn 45 is made up of a bundle of filaments or monofilaments 46 extending longitudinally thereof parallel to each other and which are retained in the bundle by a bonding band 48 which is wound therearound in a spiral. In manufacturing yarn 45, band 48 is applied thereto while molten so that it fuses with the outer filaments of the yarn with which it is in contact. This yarn has the advantage that filaments 46 do not need to be spirally wound in the yarn but can extend directly longitudinally thereof. The spiral band 48 keeps the outer filaments, with respect to strap 10, in proper place.

FIG. 4 diagrammatically illustrates the use of four bonding bands 52, 53, 54 and 55 in a strap, while FIG. diagrammatically illustrates the use of two bonding bands 57 and 58, and FIG. 6 illustrates the use on one bonding band 60. Although not absolutely necessary, it has been found desirable to use in relatively wide straps a plurality of the zigzag-bonding bands, the wider the strap, the more bands being required.

Strap can be improved by using a thread 65 formed of substantially nonextensible synthetic material which will not melt when in contact with the molten material of bonding band 18. Thread 68 can be made of nylon, fiberglass, or other suitable material that will not fuse when in contact with the molten material of the bonding band and yet which will adhere to the latter. Thread 65 is used primarily to give the strap lateral strength, and to this end it can be arranged in a zigzag pattern extending from side to side of the strap, as illustrated in FIGS. 4 to 6. It is preferable to make the zigzag arrangement of thread 65 so that it repeatedly crosses the zigzaging bonding band. Actually, portions of thread 65 are embedded in the material of the bonding band so that the thread is bonded to the inner surfaces of the yarns of the two layers where it contacts said yarn.

The yarns of strap 10 may be of a single color or of any combination of colors thereby affording wide combinations of color identification. These straps lend themselves to efficient joining by virtue of the large exposure of the individual yarns and surfaces thereof to the application of fusion bonding polyolefines or thermosetting plastic resins, These straps also lend themselves to efiicient mechanical jointing by virtue of the fact that the main tensile yarns are fully exposed to compressive forces as developed in common strap buckles, such as used widely in automotive seat belts and the like.

lclaim:

1. A synthetic strap comprising forth layers of polyolefin synthetic filament yarns extending longitudinally of the strap, the yarns of each layer being free of each other in side-by-side contact and extending substantially longitudinally of said each layer, and a relatively narrow, thin bonding band formed of polyolefin synthetic material compatible with the material of said yarns and located between the yarn layers and contacting all of the yarns thereof, said bonding band extending back and forth from side to side of the strap and leaving relatively large spaces throughout the length of the strap wherein portions of said yarns are free of said bonding band, and said bonding band having been extruded while hot directly on to the yarns being fused therewith only at contacting intersections with said yarns, whereby the band holds the yarns of each layer together and holds the layers together without interferring with the natural flexibility of the yarns.

2. A synthetic strap as claimed in claim 1 in which the filaments of each yarn are molecularly oriented.

3. A synthetic strap as claimed in claim 1 including a synthetic binder band made of material compatible with the filament material wound around the filaments of each yarn and fused only to the outer filaments thereof with which it is in contact.

4. A synthetic strap as claimed in claim 1 in which said yarns and the band are formed of polyethylene or a copolymer thereof.

5. A synthetic strap as claimed in claim 1 in which said yarns and the band are formed of polypropylene or a copolymer thereof.

6. A strap as claimed in claim 1 in which said bonding band zigzags from one side edge to the other of said strap.

7. A strap as claimed in claim 1 in which the bonding band is in the form of a plurality of spaced relatively narrow, thin bands extending generally longitudinally of the strap in zigzag patterns.

8. A synthetic strap as claimed in claim 7 in which the zigzag patterns of the bonding bands are arranged so that the bands cross each other a plurality of times throughout the length of the strap and are fused to each other at the intersections thereof.

9. A synthetic strap as claimed in claim 7 in which said bonding bands are arranged to fonn diamond-shaped openings between said yarn layers.

10. A synthetic strap as claimed in claim 9 in which one diagonal of each diamond opening extends longitudinally of the strap and is no longer than the diagonal of said each opening extending transversely of the strap.

11. A synthetic strap as claimed in claim 7 in which said yarns and the band are formed of polyethylene or a copolymer thereof.

12. A synthetic strap as claimed in claim 7 in which said yarns and the band are formed of polypropylene or a copolymer thereof.

13. A synthetic strap as claimed in claim 1 including at least one substantially nonextensible thread extending generally longitudinally of the strap in a zigzag pattern and between and contacting the yarns of the strap, said thread being formed of material that fuses at a temperature above the fusion temperature of said bonding band material and yet adheres to the latter.

14. A synthetic strap as claimed in claim 6 including at least one substantially nonextensible thread extending generally longitudinally of the strap in a zigzag pattern and between and contacting the yarns of the strap, the zigzags of the thread being arranged so that said thread repeatedly crosses the zigzag-bonding band, said thread being formed of material that fuses at a temperature above the fusion temperature of said bonding band material and yet adheres to the latter. 

2. A synthetic strap as claimed in claim 1 in which the filaments of each yarn are molecularly oriented.
 3. A synthetic strap as claimed in claim 1 iNcluding a synthetic binder band made of material compatible with the filament material wound around the filaments of each yarn and fused only to the outer filaments thereof with which it is in contact.
 4. A synthetic strap as claimed in claim 1 in which said yarns and the band are formed of polyethylene or a copolymer thereof.
 5. A synthetic strap as claimed in claim 1 in which said yarns and the band are formed of polypropylene or a copolymer thereof.
 6. A strap as claimed in claim 1 in which said bonding band zigzags from one side edge to the other of said strap.
 7. A strap as claimed in claim 1 in which the bonding band is in the form of a plurality of spaced relatively narrow, thin bands extending generally longitudinally of the strap in zigzag patterns.
 8. A synthetic strap as claimed in claim 7 in which the zigzag patterns of the bonding bands are arranged so that the bands cross each other a plurality of times throughout the length of the strap and are fused to each other at the intersections thereof.
 9. A synthetic strap as claimed in claim 7 in which said bonding bands are arranged to form diamond-shaped openings between said yarn layers.
 10. A synthetic strap as claimed in claim 9 in which one diagonal of each diamond opening extends longitudinally of the strap and is no longer than the diagonal of said each opening extending transversely of the strap.
 11. A synthetic strap as claimed in claim 7 in which said yarns and the band are formed of polyethylene or a copolymer thereof.
 12. A synthetic strap as claimed in claim 7 in which said yarns and the band are formed of polypropylene or a copolymer thereof.
 13. A synthetic strap as claimed in claim 1 including at least one substantially nonextensible thread extending generally longitudinally of the strap in a zigzag pattern and between and contacting the yarns of the strap, said thread being formed of material that fuses at a temperature above the fusion temperature of said bonding band material and yet adheres to the latter.
 14. A synthetic strap as claimed in claim 6 including at least one substantially nonextensible thread extending generally longitudinally of the strap in a zigzag pattern and between and contacting the yarns of the strap, the zigzags of the thread being arranged so that said thread repeatedly crosses the zigzag-bonding band, said thread being formed of material that fuses at a temperature above the fusion temperature of said bonding band material and yet adheres to the latter. 